1. Field of the Invention
This invention concerns a process for preparing cyclic amides. More particularly, it relates to a process for preparing cyclic amides from acetic acids and aromatic aminocarbonyl compounds.
2. The Prior Art
Cyclic amide groups appear throughout the range of organic chemistry. They may be found, for example, in monomers, in pharmaceuticals, and in a large number of synthetic and natural organic dyes and colorants. Previous methods for forming cyclic amides have included the method shown by Bunes in Belgian Pat. No. 861,945 wherein an aminoketone is reacted with a substituted acetyl chloride to give an uncyclized amide which is thereafter cyclized with base. Otteson et al, in U.S. Pat. No. 4,096,134, show the preparation of cyclic amides by the reaction of an aminoketone, i.e., a 1-aminoanthraquinone, with ethylacetoacetate in nitrobenzene. These are but two recent disclosures of representative routes. Other preparative routes to cyclic amides include the condensation of a 1-aminoanthraquinone with acetic anhydride with acid and nitrobenzene as shown by Lodge in U.S. Pat. No. 2,300,453, and the condensation of 1-aminoanthraquinone with benzoylacetic acid esters in the presence of base as shown by Peter et al, in U.S. Pat. No. 2,644,821. While all of these references produce cyclic amides, often their yields are low. This can be a serious shortcoming since the feed materials used, especially in the production of dyes or pharmaceuticals, are often complex and any yield loss can be quite costly. The process of this invention has as an advantage the achievement of very high yields of desired cyclic amide products. It has an additional advantage of proceeding faciley even at low to moderate temperatures, thus enabling the cyclic amide-functionality to be selectively introduced into molecules having other reactive groups.
As will be shown in more detail, the present process employs a promoter composed of titanium or silicon in a plus four valence state and pyridine. Some combinations of Ti(IV) and pyridine are shown in the art; e.g., Naturwischeschaften, 46, 446-7 (1959), in an article by G. S. Rao, shows TiI.sub.4 .multidot.2 pyridine and TiF.sub.4 .multidot.2 pyridine as complexes; the chloro equivalent is known, as well. It does not appear that these titanium complexes have been used as promoters for cyclic amide formation. To our knowledge, the closest reference concerning titanium may be found in the Canadian Journal of Chemistry, Vol. 48, pages 983-6, wherein TiCl.sub.4 plus alkylamines were used in the formation of noncyclic carboxamides. The presently employed pyridine complexes are not shown nor are cyclic amides produced in this reference.
3. Statement of the Invention
It has now been discovered that tetravalent titanium or silicon, [Ti(IV) or Si(IV)], in combination with pyridine or a substituted pyridine, is an effective agent for promoting the selective formation of cyclic amides from substituted or unsubstituted acetic acid, and an aromatic aminocarbonyl compound. This process enables the preparation of cyclic amides in high yield and in some cases permits the facile preparation of cyclic amides not previously preparable or preparable only with great difficulty.